May be abuse, may be burnout, may be a disgruntled client.
I've never smacked my Lab, but I have used a chain collar on her. She is not stupid, and she's certainly not mean (just assertive), but when we started training she occasionally needed a pop on the chain to get her attention. I haven't had one on her in 6 months, though, clicker training has been a great success. She still won't come when she's stolen my gardening glove though, she runs around and grins at me. Her high point was stealing one of the float bags for my kayak off the clothesline where it was drying . . . I can offer a testimonial for Dagger float bags being Lab-proof (no small feat). She got it filthy but delivered it up in exchange for a treat, and it still holds air . . . (if I was ever going to hit her, that was when! But when she came to me I couldn't hit her . . . that would be punishing her for coming to me, float bag in mouth) . . . ah, Labs!